Just get a cape pattern and then make another cape that is shorter and sew them together at the top. http://www.simplicity.com/p-2620-misses-men-teen-costumes.aspx view C is nice with another layer of a shorter cape (same pattern just shorter)

edit: this is also a lovely pattern, just make it shorter and proportional to your height! http://www.simplicity.com/p-3067-mens-costumes.aspx